The preparation of high purity crystals is of interest in a range of scientific and industrial applications; however, macroscopic and microscopic fluctuations of composition which commonly occur in solution, make it a challenge to obtain high quality crystals.
There has been considerable investigation of the effect of magnetic field on crystal growth. Several reports suggest that a magnetic field affects the growth of crystals from an aqueous solution. Thus, application of a magnetic field decreases the growth rate of ammonium dihydrogen phosphate (Zizic et al. J Crystal Growth 54:439 (1981)) and Rochelle salts (Mitrovic et al. Appl. Phys. A 51:374 (1990)). On the other hand, application of a magnetic field increases the growth rate of Fe(NH.sub.4).sub.2 (SO.sub.2).sub.2 (M. Schieber J Crystal Growth 1:131 (1967). Other studies have reported an effect of a magnetic field on phase composition in polytypic crystals (B. P. J. Prezedmojski Crystal Res. & Technol. 17:759 (1982)). In all these studies, very high magnetic field strengths in the order of 5000-20,000 Gauss (0.5-2.0 T) were applied. The effect of weak magnetic fields on crystal growth from aqueous solutions has not been investigated.
It has been known that space-grown crystals differ from those grown on Earth. As observed in the 1988 Shuttle Discovery experiment in a microgravity environment and a magnetic field which was about 80-90% of the Earth's magnetic field, lead iodide crystals grew uniformly throughout the solution and also uniformly on a membrane in the experimental chamber. This was very different from lead iodide crystals grown in laboratories on Earth, where the crystals grew only at the vertical membrane and then only at the bottom half of the membrane. Scaife et al. Chem. Mater. 2:777 (1990)!.
It is the object of the present invention to provide a method of growing crystals from solution under the combined effect of gravity and low magnetic field strengths.
It is a further object of the present invention to provide a method for crystal growth in which the growth location, size and crystal quality may be controlled.